Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

Abstract

We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v [subscript D], of Au and Zn, and put lower bounds on v [subscript D] of the other metals ranging from 10[superscript 2] to 10[superscript 4] m/s. Knowledge of v [subscript D] is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10[superscript 19] Au/cm[superscript 3] without cellular breakdown. Values of v [subscript D] are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D [subscript s](T [subscript m]), and the equilibrium partition coefficient, k [subscript e], are shown to simultaneously affect v [subscript D]. We demonstrate a correlation between v [subscript D] and the ratio D [subscript s](T [subscript m])/k [subscript e] [superscript 0.67], which is exhibited for Group III, IV, and V solutes but not for the transition metals investigated. Nevertheless, comparison with experimental results suggests that D [subscript s](T [subscript m])/k [subscript e] [superscript 0.67] might serve as a metric for evaluating the potential to supersaturate Si with transition metals by PLM.